The plane's brakes failed and it crashed into the Kali Gandaki river in the Annapurna mountain range in Nepal's northwest, Adhikari said.

"At 8:30 am (0245 GMT), the plane was landing at Jomsom airport in Mustang district when its brakes failed. Half of the aircraft's body is in the water and the other half is on the river bank," Adhikari told AFP.

"Five people, including a pilot, have been seriously injured. They are being airlifted to Pokhara for further treatment," he said, referring to the resort town where the flight originated.

The plane carried three crew members and 18 passengers.

Eight passengers were Japanese tourists en route to Jomsom, an airport town near Muktinath, a sacred Buddhist pilgrimage site at the foot of the Thorong La Himalayan mountain pass while the rest on board were Nepalese, police said.

Nepal has a poor road network and tourists, pilgrims and professional climbers often rely on the country's 16 domestic airlines and 49 airports to reach remote areas but its aviation sector has a bad safety record.

Last year, a passenger plane crashed at the same Jomsom airport, killing 15 people including 13 Indian tourists. Six people survived the crash.

Inexperienced pilots, poor management and slack regulation are jeopardising air travellers' lives in Nepal, aviation experts have warned in the wake of recent flight accidents.